The present invention relates to a self-canceller for a turn signal indicator used in motor vehicles, etc.
FIG. 3 is a partial plan view showing a conventional self canceller for a turn signal indicator. This drawing shows a state where an engaging ball 1 is engaged with a left recess 14 of a retaining element 2 with the control lever 10 (see FIG. 2) turned counterclockwise, that is, a state where the flasher indicates a left-turn. For example, engaging ball 1 has been moved from a neutral recess 15 to the left recess 14 by moving leftwards in the direction of the arrow as viewed in FIG. 2. If the steering wheel is rotated counterclockwise in this state, a cancel cam 3 rotates counterclockwise as indicated by arrow 4. When the cancel cam 3 makes contact with a cancel ratchet 5, ratchet mount 6 rotatively moves with point A as a pivot against compression spring 7. If the distance from the pivot A to the point B at which the compression spring 7 acts on the ratchet mount 6 is compared with the distance from the pivot A to the point C at which the cancel cam 3 makes contact with the cancel ratchet 5, the latter is about double the former. Therefore, according to the principles of the lever and fulcrum, about half the action force of the compression spring 7 is required for the cancel cam 3 to raise the ratchet mount 6.
After the cancel cam 3 has passed, the ratchet mount 6 is energetically returned by the action of the compression spring 7, causing the cancel ratchet 5 to collide with stopper 8. At this moment, a noise is generated, which displeases the driver of the motor vehicle.
In this construction, depending on the rotating position of the steering wheel, when the ratchet mount 6 is moved by the operation of the control lever, the cancel ratchet 5 of the ratchet mount 6 may contact and interfere with the cancel cam 3. When the control lever is operated against such interference, the ratchet mount 6 is required to act for compressing the compression spring 7. In this case, unless the control lever is operated with about half the action force of the compression spring 7 added to the control force otherwise ordinarily required, the control lever cannot be moved. Thus, depending on the rotating position of the steering wheel, the operation of the control lever becomes abnormally heavy and is a disadvantage.
Several means were proposed to decrease or remove the undesirable noise. They include the formation of a sliding slope on the cancel ratchet for easing the collision with the stopper, the formation of an elastically deformable tongue-like part in the cancel ratchet for avoiding the direct contact with the stopper, and so on.
The noise can be decreased or removed to some extent by any of those conventional means, but the latter above named problem that the operation of the control lever becomes abnormally heavy when the cancel ratchet interferes with the cancel cam is not solved.